AUTOMATIC PROCESSING

2.3.6.1 Frequency Encoding and Spatial Location Encoding 2.3.6.1.1 Clinical and nonclinical samples

There is evidence that event frequency and information about the spatial location of an object are both encoded automatically (Hasher & Zacks, 1979). Several studies have reported depressed Ss are equivalent to normal controls in their ability to judge frequency.

For example, Golinkoff and Sweeney (1989) showed Ss a list of 30 words that each appeared from one to seven times. Immediately after presentation, Ss were asked to make relative frequency judgements for 15 word-pairs taken from the list. Depressed and personality-disordered patients performed as well as normal control Ss on this task. Similar findings have been reported by Roy-Byrne et al. (1986, Procedure 2), and by Hasher and Zacks (1979, Experiment 3) who compared depressed and nondepressed community adults on the basis of a median split of their scores on the BDI. Some of these studies found the same depressed Ss to be impaired on an effortful task (Golinkoff & Sweeney, 1989; Roy-Byrne et al., 1986) which increases the strength o f these findings. Rohling and Scogin (1993) compared young and old groups of depressed patients, mixed psychiatric controls and normal controls on measures of memory for frequency and spatial location, and found no significant effects of mood. On two effortful memory tasks there were significant effects of age but not mood, weakening this finding.

2.3.6.2 Priming

A second type of task used to measure automatic processing is the priming task described in section 2.1.3.3.6.2. This paradigm permits investigation of the effects of prior experience in circumstances where Ss are not required to refer to the prior experience, and may be unable to recall it. A typical task requires Ss to carry out word-stem completion (e.g. don ) with the first idea that comes to mind; performance is facilitated by previous study of relevant items (e.g. presentation of the word 'donkey' increases the likelihood of stem completion with this word).

2.3.6.2.1 Clinical samples

Danion et al. (1991) reported depressed patients performed a word-stem completion task at normal levels, but were impaired on a measure of explicit memory. Similar findings were reported by Denny and Hunt, (1992) using a word-fragment completion test. Watkins et al. (1992) and Danion, Kauffmann-Muller, Grange, Zimmermann and Greth (1995) found depressed Ss unimpaired on both implicit and explicit measures, although Watkins et al. (1992) did report a trend toward depressive impairment on the explicit task.

Bazin, Perruchet, de Bonis and Feline (1994) noted the tasks used by Danion et al. (1991) and Denny and Hunt (1992) confound the distinction between implicit and explicit memory tasks with the provision of retrieval cues, since providing a word-fragment

essentially turns the implicit test into a cued-recall measure. Bazin et al. (1994) carried out a comparison of implicit and explicit memory tasks that differed only in their instructions, and found a dissociation, with depressed Ss impaired relative to controls only on the explicit task. Furthermore, when Ss were retested 4 weeks later, when the depressed group were clinically improved, the groups did not differ on either measure. Elliott and Greene (1992) reported depressed patients were impaired on both implicit and explicit memory measures, but Bazin et al. (1994) noted their implicit memory task procedure increased the likelihood Ss would use explicit retrieval processes.

Hertel (1994) used a word identification task in which depressed and nondepressed Ss tried to identify previously rated and unrated words that were presented briefly and masked. Hertel reported a depressive deficit in word identification when the rating task required Ss to refer to physical characteristics of the word, but not when the rating task required Ss to make a semantic judgement. Hertel interpreted these findings as suggesting depressed Ss were less likely to read the target words spontaneously (when rating physical characteristics), but when required to read the words, implicit memory was intact. The same depressed Ss were impaired relative to controls on free recall of the same words.

With regard to the studies reviewed above, the possibility cannot be excluded that explicit recall of material may have contributed to performance on the implicit memory task. Bradley et al. (1995) carried out a stringent test of implicit memory processes by introducing a subthreshold priming condition to a lexical decision task which compared neutral and emotional words. If material is presented subthreshold then any priming effect must be due to automatic processes. They found control Ss showed significantly greater priming effects for neutral words than depressed Ss in both the suprathreshold and subthreshold conditions, with the converse pattern for depression-relevant words.

2.3.6.2.2 Nonclinical samples

Several studies using nonclinical samples have found evidence of intact implicit memory with deficits in explicit memory performance in dysphoric Ss. This pattern of findings was reported by Ruiz-Caballero and Gonzalez (1994, Experiment 1) using a word-stem completion task and Hertel and Hardin (1990, Experiment 3) using a homophone spelling task. Both studies compared dysphoric and nondysphoric students selected on the basis of the BDI. Watkins, Vache, Vemey, Muller and Mathews (1996) compared students

diagnosed as depressed with nondepressed controls on a task designed to investigate conceptual rather than perceptual repetition priming. Following the presentation of the target words, Ss were required to free-associate to a series of words that were semantically related to the targets. Implicit memory was evidenced by the production of the target words during free association. Again, the dysphoric Ss were not impaired on the implict memory task.

Of the clinical studies reviewed in section 2.3.6.2.1, only Bradley et al. (1995) fully excluded the possibility that explicit recall of material contributed to performance on the implicit memory tasks. Two studies using nonclinical samples have attempted to address this issue. Bradley et al. (1994) carried out a lexical decision task similar to that of Bradley et al. (1995) (see section 2.3.6.2.1). While there was no difference between dysphoric and nondysphoric students on a suprathreshold priming task, there was a difference when the primes were presented subthreshold. The control group showed significant effects of subthreshold priming on neutral and anxious words, but not on depressed or positive words, while the dysphoric Ss showed a converse pattern. Hertel and Milan (1994), as described in section 2.3.4.2.1, used a process dissociation paradigm to separate automatic and effortful processes in recognition memory, and found dysphoric students to be unimpaired on recognition based on the automatic process of familiarity, but to be impaired on recognition based on effortful recollection of items.

In summary, the weight of evidence suggests that provided depressed Ss do process the target words (Hertel, 1994), the priming effect is intact in depressed Ss. However, the results of the studies carried out by Elliott and Greene (1992) and Bradley et al. (1994; 1995) bring a cautionary note to this conclusion. Bazin et al. (1994) noted some problems with the methodology of Elliott and Greene's (1992) study, but it is more difficult to ignore the findings of the two studies carried out by Bradley et al. (1994; 1995). The use of subthreshold presentation of target words is a powerful approach in terms o f excluding the possibility o f explicit processing of material. It is clearly important to replicate the procedures used studies that found no evidence of a depressive deficit in implicit memory using subthreshold presentation of the target words. Until this work is done, it is not possible to reach an unequivocal conclusion about priming in depression.

2.3.7 ATTENTION AND WORKING MEMORY